Magnetic resonance imaging (MRI) is a technology for imaging by use of magnetic resonance. Magnetic resonance includes that an atomic nucleus with an odd number of protons (e.g., a hydrogen atomic nucleus, which widely exists in the human body), the protons have spinning motion, like a small magnet, and the spin axes of these small magnets do not have a certain orientation. If an external magnetic field is applied, these small magnets are rearranged according to the magnetic force lines of the external magnetic field, and, more specifically, arranged in two directions that are parallel or antiparallel to the magnetic force lines of the external magnetic field. The above-mentioned direction parallel to the magnetic force lines of the external magnetic field is called a positive longitudinal axis, and the above-mentioned direction antiparallel to the magnetic force lines of the external magnetic field is called a negative longitudinal axis. The atomic nuclei only have a longitudinal magnetization component, and the longitudinal magnetization component has both direction and amplitude. Atomic nuclei in the external magnetic field are excited by a radio-frequency (RF) pulse with a specific frequency to make the spin axes of these atomic nuclei deviate from the positive longitudinal axis or the negative longitudinal axis to produce resonance. This is magnetic resonance. After the spin axes of the above-mentioned excited atomic nuclei deviate from the positive longitudinal axis or the negative longitudinal axis, the atomic nuclei will have a transverse magnetization component. After the radio-frequency pulse transmission has been stopped, the excited atomic nuclei transmit an echo signal and gradually release the absorbed energy in the form of electromagnetic waves, with the phase and energy level thereof both restoring to the state before being excited. An image may be reconstructed after the echo signal transmitted by the atomic nuclei is further processed by, for example, spatial encoding.
In the prior art, the magnetic resonance imaging system may operate with a number of various radio-frequency (RF) antennas (e.g., coils). The radio-frequency antennas are used for transmitting and receiving radio-frequency pulses so as to excite the atomic nuclei to radiate magnetic resonance signals and/or for acquiring the induced magnetic resonance signals. A magnetic resonance imaging (MRI) system includes various coils, such as a body coil covering the whole body area, a receiving coil only covering a certain part of the body and so on. The magnetic resonance system may have a large integrated coil (e.g., body coil) that is permanently fixed in a magnetic resonance scanner. The integrated coil may be arranged in a cylindrical manner surrounding a patient acquisition cavity (e.g., using a structure referred to as a birdcage structure), and in the patient acquisition cavity, a patient is supported on a bed (e.g., a patient positioning table) during measurement. Since the coverage area of the body coil is relatively large, a higher transmitting power is needed, and the signal-to-noise ratio of an obtained image is relatively low. The signal-to-noise ratio throughout the image is non-uniform as well. With respect to the body coil, the coverage area of a local coil is relatively small (e.g., the knee area covered by a knee coil, the head covered by a head coil, a wrist covered by a wrist coil), so the local coil receives only radio-frequency signals within a limited radio-frequency excitation range (in order to distinguish from the radio-frequency signals in the transmission stage, the radio-frequency signals received by the coil are hereinafter referred to as magnetic resonance signals). The signal-to-noise ratio of an obtained image is thus relatively high, and the signal-to-noise ratio throughout the image is relatively uniform.
The local coil is externally attached to the magnetic resonance imaging system. For existing magnetic resonance imaging systems, one interface may only support one local coil, and the number of interfaces configured by an early magnetic resonance system is relatively small. For an advanced application such as a later whole body image sweeping that uses a plurality of local coils simultaneously, this number of interfaces is apparently not enough. In order to make the magnetic resonance imaging system compatible with multiple local coils, a common practice is to increase the number of interfaces or to use control bus technology to send an upper-layer command to a decoder, so that the decoder controls a corresponding radio-frequency switch to switch according to the content of the command. The defects of the above method are the increase of costs of the magnetic resonance imaging system, and the original magnetic resonance imaging system that does not have enough interfaces will not be easily upgraded to a plurality of interfaces. The method that uses the control bus modifies software. The magnetic resonance imaging system has corresponding control lines and may introduce a clock signal that easily causes interference to the magnetic resonance imaging system.